[PATCH] NETFILTER: SNMP NAT: fix memory corruption (CVE-2006-2444)

CVE-2006-2444 - Potential remote DoS in SNMP NAT helper.

Fix memory corruption caused by snmp_trap_decode:

- When snmp_trap_decode fails before the id and address are allocated,
  the pointers contain random memory, but are freed by the caller
  (snmp_parse_mangle).

- When snmp_trap_decode fails after allocating just the ID, it tries
  to free both address and ID, but the address pointer still contains
  random memory. The caller frees both ID and random memory again.

- When snmp_trap_decode fails after allocating both, it frees both,
  and the callers frees both again.

The corruption can be triggered remotely when the ip_nat_snmp_basic
module is loaded and traffic on port 161 or 162 is NATed.

Found by multiple testcases of the trap-app and trap-enc groups of the
PROTOS c06-snmpv1 testsuite.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

diff --git a/net/ipv4/netfilter/ip_nat_snmp_basic.c b/net/ipv4/netfilter/ip_nat_snmp_basic.c
index 4f95d477805c051628ac2ee2fdf440d37f0b6e1c..df57e7a117dbb4c46605e44dc349ca818e58171e 100644 (file)
--- a/net/ipv4/netfilter/ip_nat_snmp_basic.c
+++ b/net/ipv4/netfilter/ip_nat_snmp_basic.c
@@ -1000,12 +1000,12 @@ static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
                
        return 1;
 
+err_addr_free:
+       kfree((unsigned long *)trap->ip_address);
+
 err_id_free:
        kfree(trap->id);
 
-err_addr_free:
-       kfree((unsigned long *)trap->ip_address);
-       
        return 0;
 }
 
@@ -1123,11 +1123,10 @@ static int snmp_parse_mangle(unsigned char *msg,
                struct snmp_v1_trap trap;
                unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
                
-               /* Discard trap allocations regardless */
-               kfree(trap.id);
-               kfree((unsigned long *)trap.ip_address);
-               
-               if (!ret)
+               if (ret) {
+                       kfree(trap.id);
+                       kfree((unsigned long *)trap.ip_address);
+               } else 
                        return ret;
                
        } else {